1. Field of the Invention
The invention relates to air-operated brake actuators of the type mounted on a bracket by means of mounting studs which extend from an actuator housing.
2. Background Art
A typical air brake system for a vehicle such as a bus, truck, or the like includes separate brake assemblies such as a brake shoe and drum at the vehicle wheels. The brake shoes are actuated in one direction to apply the brakes and in the other direction to release the brakes. The brake assemblies may serve as both service and emergency brakes, and individual brake actuators are located adjacent the wheels for actuation of the brake means.
A typical brake actuator includes a service brake actuator for applying and releasing the brakes in response to delivery and exhaust of compressed air. Often a spring brake actuator is disposed in tandem with the service brake actuator. The spring brake actuator uses the force of a strong compression spring to operate the service brake actuator and to apply the brakes when air in a spring chamber is reduced below some predetermined level. Air may be reduced in the spring brake actuator under the control of the operator in the manner of a parking brake, or automatically in emergencies such as a failure of portions of the brake air system.
Brake actuators typically employ diaphragms that move in response to air pressure and springs. The diaphragms in turn move push rods in reciprocating fashion which move the brake means between operative and inoperative positions. Typically, the push rod is pivotally attached to a slack adjuster which is splined to a camshaft having a cam which applies the brake shoes to the brake drum as the cam is rotated. The slack adjuster acts as a lever to amplify the force generated by air pressure in the brake actuator.
The brake actuator is usually mounted to the vehicle by means of a bracket securely fixed to the axle carrying the wheels to be braked. The push rod typically extends through an aperture in the brake actuator, as well as a corresponding aperture in the mounting bracket.
Various sizes of air brake actuators are available for installation on trucks and buses and the like, and the size of a unit selected for installation depends in part upon the weight of the vehicle and the number of brake assemblies to be used. Two commonly available smaller sizes in the industry are the so-called 12-inch and 16-inch actuators, with the numerals "12" and "16" typically referring to a nominal effective area in square inches of the diaphragm in the service brake chamber. A brake actuator housing is typically secured to the mounting bracket by means of mounting studs or bolts extending through the end wall of the service brake chamber on opposing sides of the push rod. The mounting studs in brake actuators sized 20-inch and above are spaced from each other a standard distance, typically 4.75 inches. On the other hand, brake actuators smaller than 20-inch have heretofore had mounting studs separated a lesser distance because of the smaller diameter of the housing.
In order to accommodate brake assembly housings of at least two different sizes, e.g., 12-inch and 16-inch, brackets have incorporated two separate sets of hole patterns to accommodate the different mounting stud spacings. The multiple unused holes on the bracket face are prime locations for surface discontinuities and stress risers which tend to shorten the useful life of the brackets. It would be advantageous to extend the standard spacing of mounting studs to smaller-sized brake actuators, and thus eliminate the need for additional holes on the mounting bracket. In addition, consolidation of attachment hardware to one size can be achieved.